Nitrogen-containing compounds as corrosion inhibitors

ABSTRACT

The present invention relates to nitrogen-containing hydroxyethyl substituted compounds to be used as corrosion inhibitors for metal surfaces, for example in aqueous systems and in particular in oil-field applications, e.g. in oil or gas wells, and which could be used under sweet-well conditions as well as under sour-well conditions. It may also be used in oil-field acidizing and fracture-acidizing well stimulation treatment. The compounds belong to the group of partly ethoxylated fatty alkylamines, partly ethoxylated alkyletheramines and partly or fully hydroxyethyl substituted alkylamdopropylamines. The corrosion inhibitors have the formula (I) where R is a hydrocarbyl or an acyl group having 14-24 carbon atoms, or the group R′OCH 2 CH 2 CH 2  where R′ is a hydrocarbyl group with 14-24 carbon atoms; X is hydrogen, C 2 H 4 OH or the group Y is hydrogen or C 2 H 4 OH and n is 0-3, with the proviso that at least one of the symbols X and Y is C 2 H 4 OH, at most one of the symbols X is n is at least one when R is an acyl group, and when R is a hydrocarbyl group or the group R′OCH 2 CH 2 CH 2  at least one of the symbols X and Y is hydrogen.

The present invention relates to nitrogen-containing hydroxyethyl substituted compounds to be used as corrosion inhibitors for metal surfaces, for example in aqueous systems and in particular in oil-field applications, e.g. in oil or gas wells, and which could be used under sweet-well conditions as well as under sour-well conditions. It may also be used in oil-field acidizing and fracture-acidizing well stimulation treatment. The compounds belong to the group of partly ethoxylated fatty alkylamines, partly ethoxylated alkyletheramines and partly or fully hydroxyethyl substituted alkylamidopropylamines.

The use of amines as corrosion inhibitors in different kinds of systems is well known. Also ethoxylated amines have been described as components in rust inhibiting compositions, as for example in U.S. Pat. No. 3,977,994 where a rust inhibiting composition for metal surfaces is disclosed. This composition contains a C16-C20 organic acid and a C3-C12 N-alkyl or N-cycloalkyl-substituted ethanolamine.

In EP-A1-750 033 a hydraulic fluid composition based on a boric ester of a glycol ether is disclosed, which comprises a corrosion-inhibiting system that includes at least one constituent chosen from fatty mono- di- or polyamines, optionally ethoxylated in all active positions, or the salts of one or more carboxylic acids with the said amines, and esters between one or more carboxylic fatty acids and a polyoxyalkylene glycol.

EP-A2-903398 describes a method for increasing the corrosion resistance of a lubricating grease, by the addition of a minor portion of one or more alkoxylated C1-C30 alkylamines containing from 0 to 50 moles of alkoxide. All working examples describe compositions containing alkoxylated fatty amines where all active positions were substituted with ethylene oxide. Particularly preferred was the tallow amine derivative with 5 moles of ethylene oxide.

BE 841 567 and BE 841 536 disclose N-alkyl-aminoalkanols where the alkyl chain carries a hydroxy substituent, said compounds being obtained from (α-olefin epoxides and amines or aminoalkanols. These compounds work as corrosion inhibitors in an aqueous environment.

In JP 58091176-A N-alkyl substituted alkanolamines with one or two alkyl chains containing a total of less than 7 carbon atoms are described as anti-corrosion additives for calcium chloride brine systems. Among the compounds specifically mentioned are 2-ethylaminoethanol, 2-n-butyl-aminoethanol, 2-dimethylaminoethanol and 2-diethylaminoethanol. The compounds could also be used in the presence of a triazole.

In JP 58021488-A an aqueous hydraulic fluid composition is disclosed that comprises a sorbitan ester, an alkoxylated alkylamide, an alkoxylated alkylmonoamine or an alkoxylated alkylpropylenediamine and water. This hydraulic fluid exhibits a suitable viscosity and does not rust. The amines disclosed in the working examples were oleylamine+5EO or N-(tallow alkyl)propylenediamine+5EO, where all active positions are substituted by ethylene oxide.

In U.S. Pat. No. 3,029,125 a process for inhibiting corrosion in steam and condensate return systems is disclosed, where alkylene diamines with a hydrocarbyl chain containing 10 to 32 carbon atoms, and that have been hydroxyalkylated with from 1 to 4 moles of a lower alkylene oxide, are used as corrosion inhibitors. It is stated in column 6 lines 66-71 that optimum results in evaluating compositions provided in accordance with the invention have been obtained with fully oxyalkylated long chain hydrocarbon polyamines in which all of the active hydrogen atoms attached to nitrogen atoms have been substituted by hydroxy lower alkyl groups.

Although a variety of corrosion inhibitors to be used in the presence of freshwater, seawater or brine has been developed, there is still a need for more effective corrosion inhibitors and compositions, especially with the strenuous conditions prevailing in oil-well applications.

It has now surprisingly been found that a hydroxyethyl substituted amine having the formula

where R is a hydrocarbyl or an acyl group having 14-24, preferably 16-22, carbon atoms, or the group R′OCH₂CH₂CH₂ where R′ is a hydrocarbyl group with 14-24, preferably 16-22, carbon atoms; X is hydrogen, C₂H₄OH or the group

Y is hydrogen or C₂H₄OH and n is 0-3, preferably 0-2 and most preferably 1-2, with the proviso that at least one of the symbols X and Y is C₂H₄OH, at most one of the symbols X is

n is at least one when R is an acyl group, and when R is a hydrocarbyl group or the group R′OCH₂CH₂CH₂ at least one of the symbols X and Y is hydrogen; can be used as a corrosion inhibitor for metal surfaces, e.g. in aqueous environments. Various metals, such as iron, copper, zinc, aluminium and cobalt, as well as alloys, such as brass and iron-containing alloys, can be protected by said compounds. In addition they also inhibit scale formation.

The hydroxyethyl substituted alkylamines or alkyletheramines of formula (I) are only partly substituted, i.e. not all nitrogen positions containing active hydrogen atoms are substituted by hydroxyethyl or polyethylene glycol groups. These compounds are preferably obtained by ethoxylation of alkylamines or alkyl etheramines, and will hereafter be referred to as partly ethoxylated amines. It has surprisingly been found that the said amines have a much better corrosion-inhibiting ability than the corresponding unethoxylated or fully ethoxylated amines, where the phrase “fully ethoxylated amines” refer to amines where all nitrogen positions containing active hydrogen atoms are substituted by hydroxyethyl or polyethylene glycol groups.

Suitable examples of the corrosion inhibitors according to the present invention are the ethoxylated alkylamines of formula I, where R is a hydrocarbyl group having 14-24, preferably 16-22, carbon atoms, and X, Y, and n have the same meaning as above.

Suitable examples of alkylamines that could be used as starting materials for the ethoxylated alkylamines are fatty monoamines according to the formula R1NH₂ (II), where R1 is an aliphatic group having 14-24, preferably 16-22 carbon atoms; fatty diamines according to the formula R2NHCH₂CH₂CH₂NH₂ (III), where R2 is an aliphatic group having 14-24, preferably 16-22 carbon atoms; linear fatty triamines according to the formula R3NHCH₂CH₂CH₂NHCH₂CH₂CH₂NH₂ (IV), where R3 is an aliphatic group having 14-24, preferably 16-22 carbon atoms; and branched fatty triamines (Y-triamines) according to the formula R4N(CH₂CH₂CH₂NH₂)₂ (V), where R4 is an aliphatic group having 14-24, preferably 16-22 carbon atoms. The degree of hydroxyethyl molecular substitution for the alkylamine corrosion inhibitors of the present invention varies between 1 up to z−1, where z is the number of active hydrogen atoms attached to the amino groups. Consequently, when speaking of specific corrosion inhibiting amino compounds, the indicated number of ethylene oxide units added to an amino compound is the average of the number of hydroxyethyl groups introduced into the molecule.

Suitable examples of ethoxylated amines according to the present invention is oleylamine+1EO, (tallow alkyl)amine+1EO, (rape seed alkyl)amine+1EO, (soya alkyl)amine+1EO, erucylamine+1EO, N-oleyl-trimethylenediamine+1EO, N-(tallow alkyl)trimethylenediamine+1EO, N-(rape seed alkyl)trimethylenediamine+1EO, N-(soya alkyl)trimethylenediamine+1EO, N-erucyl-trimethylenediamine+1EO, N-(tallow alkyl)trimethylenediamine+2EO, N-oleyl-trimethylenediamine+2EO, N-(rape seed alkyl)trimethylenediamine+2EO, N-(soya alkyl)trimethylenediamine+2EO, N-erucyl-trimethylenediamine+2EO, N,N-bis(3-aminopropyl) (rape seed alkyl)amine+1EO, N,N-bis(3-aminopropyl) (rape seed alkyl)amine+2EO, N,N-bis(3-aminopropyl) (rape seed alkyl)amine+3EO, N,N-bis(3-aminopropyl) (tallow alkyl)amine+1EO, N,N-bis(3-aminopropyl) (tallow alkyl)amine+2EO, N,N-bis(3-aminopropyl) (tallow alkyl)amine+3EO, N,N-bis(3-aminopropyl) (soya alkyl)amine+1EO, N,N-bis(3-aminopropyl) (soya alkyl)amine+2EO, N,N-bis(3-aminopropyl) (soya alkyl)amine+3EO, N,N-bis(3-aminopropyl)oleylamine+1EO, N,N-bis(3-aminopropyl)oleylamine+2EO, N,N-bis(3-aminopropyl)oleylamine+3EO, N-oleyl-N′-(3-aminopropyl)-1,3-propanediamine+1EO, N-oleyl-N′-(3-aminopropyl)-1,3-propanediamine+2EO, N-oleyl-N′-(3-aminopropyl)-1,3-propanediamine+3EO, N-(tallow alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+1EO, N-(tallow alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+2EO, N-(tallow alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+3EO, N-(rape seed alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+1EO, N-(rape seed alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+2EO, N-(rape seed alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+3EO, N-(soya alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+1EO, N-(soya alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+2EO, N-(soya alkyl)-N′-(3-aminopropyl)-1,3-propanediamine+3EO, N-(3-aminopropyl)-N′-[3-(9-octadecenylamino)propyl]-1,3-propanediamine+1EO, N-(3-aminopropyl)-N′-[3-(9-octadecenylamino)propyl]-1,3-propanediamine+2EO, N-(3-aminopropyl)-N′-[3-(9-octadecenylamino)propyl]-1,3-propanediamine+3EO, N-(3-aminopropyl)-N′-[3-(9-octadecenylamino)propyl]-1,3-propanediamine+4EO, N-(3-aminopropyl)-N′-[3-(rape seed alkylamino)propyl]-1,3-propanediamine+1EO, N-(3-aminopropyl)-N′-[3-(rape seed alkylamino)propyl]-1,3-propanediamine+2EO, N-(3-aminopropyl)-N′-[3-(rape seed alkylamino)propyl]-1,3-propanediamine+3EO and N-(3-aminopropyl)-N′-[3-(rape seed alkylamino)propyl]-1,3-propanediamine+4EO.

Other examples of suitable corrosion inhibitors according to the present invention are the ethoxylated alkyl etheramines of formula I, where R is the group R′OCH₂CH₂CH₂ where R′ is a hydrocarbyl group with 14-24, preferably 16-22, carbon atoms, and X, Y, and n have the same meaning as above.

Suitable examples of alkyl etheramines that could be used as starting materials for the ethoxylated alkyl etheramines are R′OCH₂CH₂CH₂NH₂ (VI) and R′OCH₂CH₂CH₂NHCH₂CH₂CH₂NH₂ (VII). Especially preferred examples of the ethoxylated alkyl etheramines are R′OCH₂CH₂CH₂NH₂+1EO, R′OCH₂CH₂CH₂NHCH₂CH₂CH₂NH₂+1EO and R′OCH₂CH₂CH₂NHCH₂CH₂CH₂NH₂+2EO, where R′ is a hydrocarbyl group with 14-24, preferably 16-22, carbon atoms, e.g. tallow alkyl, soya alkyl, rape seed alkyl, octadecenyl or erucyl.

Further suitable examples of corrosion inhibitors according to the present invention are the amidoamines of formula I, where R is an acyl group having 14-24, preferably 16-22, carbon atoms, and X, Y, and n have the same meaning as above, and at least one of the symbols X and Y is CH₂CH₂OH. More preferred are the compounds where at least one of the symbols X and Y is hydrogen. The most preferred alkyl amidoamines are the monoamido monoamines

where Y is H or C₂H₄OH, provided that at least one Y is C₂H₄OH, and preferably at least one of the symbols Y is hydrogen. Examples of compounds VIII are the tallow or rape seed amide of N,N-bishydroxyethyl-1,3-propylenediamine, obtainable from the said amine and tallow or rape seed fatty acid respectively. Especially preferred aminoamides are the monoamido monoamines R″(C═O)NHCH₂CH₂CH₂NHCH₂CH₂OH (IX), obtainable from N-hydroxyethyl-1,3-propylenediamine and a fatty acid, such as rape seed fatty acid, soya fatty acid, tallow fatty acid, octadecenoic acid or erucic acid.

When producing the corrosion inhibitors of the present invention by ethoxylation of starting materials containing one or more amino groups, there will invariably be obtained mixtures of ethoxylated species with a different degree of substitution. These mixtures of ethoxylated amines, that contain the hydroxyethyl substituted amines of the invention, will normally contain a total of 10-50%, preferably 10-40% and most preferably 10-35% of primary amino groups, 10-70%, preferably 25-65% and most preferably 30-60% is of secondary amino groups, and 10-50%, preferably 20-40% and most preferably 25-35% of tertiary amino groups. For example, when a fatty monoamine according to the formula R1NH₂ (II) is reacted with 1 mole of ethylene oxide, the result will be a mixture of ca 33% of unreacted primary amine, 33% of a secondary amine R1NHCH₂CH₂OH and 33% of a tertiary amine R1N(CH₂CH₂OH)₂. When a fatty diamine according to the formula R2NHCH₂CH₂CH₂NH₂ (III) is reacted with 1 mole of ethylene oxide, the mixture obtained will contain products with a total of 33% primary amino groups, 35% secondary amino groups and 31% tertiary amino groups. For a product obtained when a fatty diamine is reacted with 2 moles of ethylene oxide the distribution will be 12% primary amino groups, 54% secondary amino groups and 34% tertiary amino groups.

For corrosion, an especially severe environment is encountered in gas- and oil-field applications, in particular where work is done off-shore or on the coast, and where carbon dioxide or hydrogen sulfide corrosion of ferrous metal surfaces is particularly troublesome. Even more severe conditions apply when acid is added in oil-field acidizing and fracture-acidizing well stimulation treatments. The corrosion inhibitors of the present invention may be used under sweet-well conditions (brine containing carbon dioxide) as well as under sour-well conditions (H₂S present), and with water solutions containing acid. The corrosion inhibitors will protect the metal surfaces of pipelines, pumps and other equipment used in the oil wells. The metals to be protected from corrosion by the corrosion inhibitors are preferably ferrous metals, such as iron and steel. The corrosion inhibitors may also work as scale inhibitors.

The amount of the amine corrosion inhibitor that is required to obtain a sufficient corrosion protection may vary with the application where it is used, but is suitably between 2% (w/w) and 2 ppm, preferably between 500 and 2 ppm and most preferably between 120 and 2 ppm.

In addition to the amine corrosion inhibitors of the present invention, other ingredients could be added to the corrosion inhibiting compositions. Examples of such ingredients are organic or inorganic acids, such as acetic acid, citric acid, hydrochloric acid and hydrofluoric acid, in which case the amines will be present as salts; a dispersing surfactant, such as nonionic ethylene oxide adducts; water-miscible solvents, such as methanol, ethanol, isopropanol or glycols; scale inhibitors; biocides, such as quaternary ammonium compounds, e.g. alkyl trimethylammmonium chlorides; gelling or viscosity-enhancing agents, such as alkyldimethylamine oxides, alkylamidopropyldimethylamine oxides or quaternary ammonium salts, e.g. alkylbis(hydroxyethyl)methyl quaternary ammonium chloride; and other corrosion inhibitors, such as other amines, amides, or amphoterics.

The following embodiments illustrate the invention, and they should not be construed as limiting the scope thereof.

EXAMPLE 1

The following compounds were assessed for their substantivity by an ellipsometric technique. In this technique silicon wafers coated with chromium were placed in an ellipsometric cell and a solution of the substances in water was added (active concentration=100 ppm). The adsorption onto chromium was followed for at least 30 minutes, and the adsorbed mass was calculated. TABLE 1 Adsorbed mass Compound (mg/m²) (Coco alkyl)amine (Comparison) 1.85 (Tallow alkyl)amine (Comparison) 2.01 (Rape seed alkyl)amine* (Comparison) 2.04 (Rape seed alkyl)amine* + 1EO 8.50 N-(Coco alkyl)trimethylenediamine (Comparison) 2.07 N-(Coco alkyl)trimethylenediamine + 1EO 4.5 (Comparison) N-(Coco alkyl)trimethylenediamine + 2EO 3.7 (Comparison) N-(Coco alkyl)trimethylenediamine + 3EO 2.7 (Comparison) N-(Tallow alkyl)trimethylenediamine 1.89 (Comparison) N-(Tallow alkyl)trimethylenediamine + 1EO 5.2 N-(Tallow alkyl)trimethylenediamine + 2EO 4.3 N-(Tallow alkyl)trimethylenediamine + 3EO 1.3 (Comparison) N-(Rape seed alkyl)*trimethylenediamine 2.41 (Comparison) N-(Rape seed alkyl)*trimethylenediamine + 1EO 4.6 N-(Rape seed alkyl)*trimethylenediamine + 2EO 4.5 N,N-bis(3-aminopropyl)(tallow alkyl)amine 0.92 (Comparison) N,N-bis(3-aminopropyl)(tallow alkyl)amine + 1EO 5.04 N,N-bis(3-aminopropyl)(tallow alkyl)amine + 2EO 4.64 N,N-bis(3-aminopropyl)(tallow alkyl)amine + 3EO 4.53 *from low erucic rape seed oil From Table 1 it is evident that the adsorbed mass is greater when the amine has greater secondary characteristics. If the amine is fully substituted with ethylene oxide, to give an amine with tertiary characteristics, or if the amine is not substituted with ethylene oxide at all, the level of adsorption falls below that of a partially substituted amine. A low adsorption would mean that the compound is unlikely to be effective as a corrosion inhibitor.

EXAMPLE 2

A series of corrosion measurements were performed by the “bubble test method”. In these a simulated “Forties” brine was used (Forties is an oil-field in the North Sea), which was saturated with CO₂ (pH ca 5.3), the test electrodes were typical pipeline steel (Grade API 5L X52 polished to 600 grit finish), the temperature was 50° C., and the solution was continuously stirred.

Forties Brine Composition:

Quantity of salts for 1 litre of simulated Forties brine Na₂SO₄ 0.016 g NaCl 74.14 g NaHCO₃ 0.68 g MgCl₂*6H₂O 4.21 g CaCl₂*6H₂O 17.19 g KCl 0.71 g Procedure: The brine solution was introduced into the test vessel, and the vessel was de-aerated by purging with CO₂ overnight. The temperature was then set at 50° C., and the pressure of CO₂ was kept at 1 bar. The polished electrode was degreased, rinsed and dried, after which it was put into the electrode holder and inserted into the test cell. The magnetic stirrer was started and a baseline corrosion rate was established by measuring the Linear Polarisation Resistance every 30 minutes (4-5 hours). Then the compounds to be investigated were introduced by injection into the solution at the concentrations specified in Table 2 using a micropipette. The corrosion rate was followed until it stabilised. The % protection was then calculated from the following equation: % protection=(1−(x/y))*100 where

-   -   x=corrosion rate in the presence of corrosion inhibitor         (mm/year)

y=corrosion rate in the absence of corrosion inhibitor (mm/year) TABLE 2 % protection Compound 10 ppm 50 ppm 100 ppm (Tallow alkyl)amine + 1EO 89.7 86 (Rape seed alkyl) *amine + 1EO 91.4 92 94.5 N-(Coco alkyl)trimethylenediamine + 1EO −20.3 (Comparison) N-(Coco alkyl)trimethylenediamine + 2EO −28.7 (Comparison) N-(Tallow alkyl)trimethylenediamine + 85 89.5 93.5 1EO N-(Tallow alkyl)trimethylenediamine + 77.1 87 89.5 2EO N-(Rape seed alkyl) *- 94.7 96 trimethylenediamine + 1EO N-(Rape seed alkyl) *- 93 98.7 trimethylenediamine + 2EO N,N-bis(3-aminopropyl)(rape 81.1 seed alkyl)*amine + 2EO N-(Rape seed alkyl) **- 90.7 trimethylenediamine + 1EO N-(Rape seed alkyl) **- 82.3 trimethylenediamine + 2EO *from low erucic rape seed oil **from high erucic rape seed oil

The table shows that particularly good protection is obtained with compounds having long alkyl groups with a high degree of unsaturation. For example the N-(Rape seed alkyl)trimethylenediamine+1 or 2EO (derived from low erucic rape seed oil) afford an excellent corrosion protection, which is very surprising since the comparative examples with products containing a coco alkyl chain do not afford any protection at all.

EXAMPLE 3

Corrosion measurements for some hydroxyethyl substituted aminoamides were performed by the same procedure as described in Example 2. TABLE 3 % protection Compound 10 ppm 50 ppm 100 ppm Tallow-CONH(CH₂)₃NHCH₂CH₂OH 78.0 96.0 97.5 Tallow-CONH(CH₂)₃N(CH₂CH₂OH)₂ 59.5 93.5 93.5 Both of the aminoamide compounds in the table above are very efficient as corrosion inhibitors at 50 ppm and higher. During the test conditions the aminoamide compound where the amino group nitrogen is secondary is somewhat more efficient, especially at low concentrations, than the aminoamide compound where the amino group nitrogen is tertiary.

EXAMPLE 4

Corrosion rate measurements were performed under more severe conditions, where the electrodes were suspended in a rotating cage in an autoclave. The brine solution composition was the same as in example 2. The electrode was prepared from API 5L X52 grade steel and polished to 600 grit. The temperature was kept at 80° C., and the vessel was pressurized with 2 bar of CO₂.

Procedure:

The electrode was placed in the cell, and the cell was flushed with CO₂. The brine solution, that had been de-aerated, was transferred into the cell under a CO₂ blanket. The rotation speed was set to achieve the required wall shear stress. The temperature was set at 80° C., and the cell was continuously purged with CO₂. A baseline corrosion rate was established by measuring the Linear Polarisation Resistance. When a stable baseline had been established, the compounds to be investigated were introduced by injection into the solution at the concentrations specified in Table 4 using a micropipette. The corrosion rate was followed until it stabilised. The % protection was calculated by the equation used in examples 2 and 3.

As a comparison N-(Tallow alkyl)-trimethylenediamine+3EO, which is mentioned as one preferred compound in U.S. Pat. No. 3,029,125, was used. TABLE 4 % protection Compound 50 ppm 100 ppm 150 ppm (Rape seed alkyl) *amine + 1EO 95.0 95.0 95.0 N-(Rape seed alkyl) *- 90.5 95.0 91.0 trimethylenediamine + 1EO N-(Rape seed alkyl) *- 95.0 95.0 95.5 trimethylenediamine + 2EO N-(Tallow alkyl)-trimethylenediamine + 65.9 70.7** 3EO (comparison) Tallow-CONH(CH₂)₃NHCH₂CH₂OH 94.5 98.0 98.0 (Rape seed) 95.1 97.8 98.4 *—CONH(CH₂)₃NHCH₂CH₂OH (Rape seed) 92.7 93.7 95.0 *—CONH(CH₂)₃N(CH₂CH₂OH)₂ *from low erucic rape seed oil **measured at 200 ppm

The hydroxyethyl substituted amines according to the invention exhibited excellent corrosion protection also under the severe conditions prevailing in this test. The comparison test showed that the corrosion protection obtained by the prior art compound was inferior to the protection obtained from the compounds according to the invention. 

1. A corrosion inhibitor for metal surfaces in an aqueous environment in oil-field applications which comprises at least one hydroxyethyl substituted amine having the formula

where R is a hydrocarbyl or an acyl group having 14-24 carbon atoms, or the group R′OCH₂CH₂CH₂ where R′ is a hydrocarbyl group with 14-24 carbon atoms; X is hydrogen, C₂H₄OH or the group

Y is hydrogen or C₂H₄OH and n is 0-3, with the proviso that at least one of the symbols X and Y is C₂H₄OH, at most one of the symbols X is

n is at least one when R is an acyl group, and when R is a hydrocarbyl group or the group R′OCH₂CH₂CH₂ at least one of the symbols X and Y is hydrogen.
 2. The corrosion inhibitor of claim 1, where R is a hydrocarbyl group having 16-22 carbon atoms.
 3. The corrosion inhibitor of claim 1, where n is 0-2.
 4. The corrosion inhibitor of claim 1, where n is 1-2.
 5. The corrosion inhibitor of claim 1, where R is the group R′OCH₂CH₂CH₂, where R′ has the same meaning as in claim
 1. 6. The corrosion inhibitor of claim 1, where R is an acyl group with 14-24 carbon atoms and at least one of the symbols X and Y is hydrogen.
 7. The corrosion inhibitor of claim 1 wherein said amine is of the formula R″(C═O)NHCH₂CH₂CH₂NHCH₂CH₂OH  (VI) where R″(C═O) is an acyl group with 14-24 carbon atoms.
 8. The corrosion inhibitor of claim 1 wherein said aqueous environment is acidic.
 9. The corrosion inhibitor of claim 1 wherein said oilfield application is under sweet-well conditions.
 10. The corrosion inhibitor of claim 1 wherein said oilfield application is under sour-well conditions.
 11. The corrosion inhibitor of claim 1 which comprises a mixture of ethoxylated amines, wherein the said mixture contains a total of 10-50% of primary amino groups, 10-70% of secondary amino groups and 10-50% of tertiary amino groups.
 12. The corrosion inhibitor of claim 11, wherein the said mixture contains a total of 10-40% of primary amino groups, 25-65% of secondary amino groups and 20-40% of tertiary amino groups.
 13. The corrosion inhibitor of claim 12, wherein the said mixture contains a total of 10-35% of primary amino groups, 30-60% of secondary amino groups and 25-35% of tertiary amino groups.
 14. A method for the inhibition of corrosion on ferrous metal surfaces in an aqueous environment, wherein said method comprises adding to said environment and/or contacting said ferrous metal surface with a corrosion inhibiting effective amount of at least one hydroxyethyl substituted amine having the formula

where R is a hydrocarbyl or an acyl group having 14-24 carbon atoms, or the group R′OCH₂CH₂CH₂ where R′ is a hydrocarbyl group with 14-24 carbon atoms; X is hydrogen, C₂H₄OH or the group

Y is hydrogen or C₂H₄OH and n is 0-3, with the proviso that at least one of the symbols X and Y is C₂H₄OH, at most one of the symbols X is

n is at least one when R is an acyl group, and when R is a hydrocarbyl group or the group R′OCH₂CH₂CH₂ at least one of the symbols X and Y is hydrogen.
 15. The method of claim 14, where R is a hydrocarbyl group having 16-22 carbon atoms.
 16. The method of claim 14, where n is 0-2.
 17. The method of claim 16, where n is 1-2.
 18. The method of claim 14, where R is the group R′OCH₂CH₂CH₂, where R has the same meaning as in claim
 14. 19. The method of claim 14, where R is an acyl group with 14-24 carbon atoms and at least one of the symbols X and Y is hydrogen.
 20. The method of claim 1 wherein said amine is of the formula R″(C═O)NHCH₂CH₂CH₂NHCH₂CH₂OH  (VI) where R″(C═O) is an acyl group with 14-24 carbon atoms. 